This invention relates to a diagnostic system and a test stand apparatus to test, calibrate and troubleshoot motor operated valve actuators. It relates particularly to a diagnostic system and test stand apparatus that is able to measure, test, calibrate and analyze several important operating parameters associated with motor operated valve actuators. The invention is especially useful in the field of valve diagnostics.
In the nuclear power industry, valves are often actuated remotely by electric motors to open, closed and intermediate positions to improve or maintain power plant output and to maintain proper cooling of the nuclear reactor. Continuous and proper operation of the valves is essential for reliable operation of the power plant and safety of the general public. Motor operated valves are also used extensively in industries other than the nuclear power industry that also require continuous and reliable operation of the valve at all times.
The valve user industries and the valve manufacturing industry have had a need to develop apparatus, methods and systems to measure, test, and calibrate various operating parameters associated with the valves and to detect any significant changes or problems in any of the operating parameters being measured that could affect the continuous and reliable operation of the valve while it is in service.
U.S. Pat. No. 4,542,649 to Charbonneau et al. discloses a recently developed valve testing system for an electric motor operated valve that measures, records and correlates a number of valve operating parameters, such as valve stem load, valve stem movements, valve stem torque, spring pack movement and motor current. The information provided by the system described in the Charbonneau et al. patent provides a direct indication to the operator or test engineer of any valve problems, such as excessive or inadequate packing loads, excessive inertia, incorrectly set limit and torque switches, malfunctioning thermal overload devices, excessive stem thrust loads, gear train wear and damage to the valve stem.
As a result of the teachings of the Charbonneau et al. patent, efforts have been made by Movats, Inc., the assignee of the Charbonneau et al. patent, as well as the assignee of the present patent application, to develop additional apparatus, testing methods and systems by which the operation and performance of different types of valves and valve components could be easily measured, tested and evaluated. U.S. Pat. Nos. 4,759,224; 4,860,596; 5,140,853 and 5,142,906 describe several of the valve diagnostic systems developed by Movats, Inc. U.S. Pat. Nos. 4,498,336; 4,570,903; 4,856,327; 4,879,901; 4,977,782 and 5,174,152 describe several of the valve diagnostic systems developed by others working in this field.
In the past, valves and especially those operated by an electric motor, called an "MOV", were usually tested while in service in the field by one or more of the valve testing and diagnostic systems described in the above-noted prior patents. Two very important operating parameters of a MOV that need to be regularly tested, measured and calibrated are the torque and axial thrust produced by the electric motor driven valve actuator that is attached to the valve stem used to operate the valve to an open, closed or intermediate position. While several of the valve testing systems described in the above-noted prior patents are able to measure the torque and axial thrust acting on the valve stem while the valve is in actual service in the field, none of the prior art valve testing systems are capable of measuring the torque and and axial thrust produced by the valve actuator and acting on the valve stem while the valve stem, or its substitute equivalent drive shaft, is under actively adjustable, controllable and measurable axial and torsional loads.